Anterior cervical plating system and bone screw

ABSTRACT

Anatomically contoured anterior cervical plates with bone ingrowth surfaces, providing for intersegmental compressive preloading, and a rigid and locked interface to all of the bone screws, with those engaging the vertebrae deployed in highly convergent pairs. The bone screws have a tapered self-tapping leading end, an increasing root diameter with a generally constant outer diameter with a thread that is narrow and sharp throughout and an enlarged head portion capable of an interference fit to the receiving holes of the plate. Instrumentation consists of plate holders, a compression apparatus and a pilot hole forming device that interlocks with the plate. Methods for spinal compression and bone hole preparation are provided.

1. RELATED APPLICATIONS

[0001] This application is a divisional of application Ser. No.09/618,036, filed Jul. 17, 2000; which is a divisional of applicationSer. No. 09/022,293, filed Feb. 11, 1998; and claims priority of U.S.provisional application Serial No. 60/037,139, filed Feb. 11, 1997; allof which are incorporated herein by reference. application Ser. No.09/022,344, filed Feb. 11, 1998, and titled SKELETAL PLATING SYSTEM, NowU.S. Pat. No. 6,139,550, is incorporated herein by reference.

BACKGROUND OF THE INVENTION

[0002] 1. Field of the Invention

[0003] The present invention relates generally to implants, method, andinstrumentation for fusion of the human cervical spine from the anterioraspect, and in particular to plate systems for aligning and maintainingadjacent cervical vertebrae in a selected spatial relationship duringspinal fusion of those vertebrae.

[0004] 2. Description of the Related Art

[0005] It is current practice in the art to use cervical plating systemsfor this purpose. Such systems are composed essentially of plates andscrews for aligning and holding vertebrae in a desired position relativeto one another. The earliest such devices consisted of stainless steelplates and screws and required that the screws passed entirely throughthe vertebrae and into the spinal canal in order to engage the strongbone tissue (the posterior cortex) of the vertebral bodies. Thisrequired the ability to observe or visualize this area radiographically,which is not always possible, especially in the lower cervical spinewhere the vertebrae may be hidden radiographically by the shoulders.

[0006] In order to form holes in the vertebral bodies for insertion ofeach screw, a drilling operation was performed, followed by a tappingoperation. Each of these operations involved the passage of aninstrument entirely through the associated vertebral body and into thespinal column. Thus, these instruments come into close proximity to thespinal cord and the dural sac which are in close proximity to the backsurfaces of the vertebral bodies. Any procedure which introduces anobject into the spinal canal presents serious risks which are of concernto the surgeon.

[0007] The conventional technique of forming a bone screw receiving holein vertebral bodies by drilling has a number of significantdisadvantages. For example, drilling removes bone material, leaving avoid and resulting in a loss of bone material. Drilling also causesmicrofracturing of the bone at the drill bit-bone interface and theresulting fracture lines tend to propagate in directions perpendicularto the wall of the hole. More specifically, the bone material isessentially a type of ceramic which exhibits a brittle pattern offracture formation and propagation in response to drilling. Furthermore,drilling generates heat which can result in thermal necrosis of the bonematerial precisely at the interface between the bone and a subsequentlyinstalled screw, where necrosis is most harmful. Any bone which doesexperience necrosis will subsequently be resorbed by the body as part ofthe bone repair process and this can lead to the loosening of the screw.

[0008] Another problem with drilling is that the path of the drill bitis difficult to control and since the drill bit operates by rotation, itcan wind up soft tissue about the associated plate. In addition, unlessgreat care is taken, the drill bit may be driven significantly past theposterior cortex and cause irreparable harm within the spinal canal.Finally, a drill bit may bind and fracture within the vertebral body andcan then cause serious injury as the still rotating portion of the drillbit passes into the wound, while the portion of the bit which has brokenoff may either protrude dangerously from the vertebral body or may bebroken off flush with the upper surface of the body so as to beirretrievably embedded therein. In any event, the steps that must betaken to retrieve the broken-off portion of a drill bit will inevitablyprolong and complicate the surgical procedure.

[0009] In known plating systems, there have been problems with looseningand failure of the hardware, breakage of the screws and plates, andbacking out of screws into the patient's throat area. These occurrencesgenerally require further surgical procedures to replace the brokenparts or the plates and screws entirely, and to repair any damage thatmay have been caused.

[0010] Other problems which have been encountered with known systemsresult from the failure of the screws to achieve a sufficient purchasein the bone and the stripping of the screws. Also, the use of the knownplating systems may result in a loss of lordosis, which is the normalcurve of the cervical spine when viewed from the side.

[0011] Known plating systems additionally experience problems inconnection with those procedures where bone grafts are placed betweenvertebral bodies to achieve an interbody fusion which heals by a processcalled “creeping substitution”. In this process, bone at the interfacebetween the graft and a vertebra is removed by a biological processwhich involves the production of powerful acids and enzymes, as aprelude to invasion of the interface by living tissue and thedeposition, or growth, of new bone. While the plates allow for properalignment of the vertebrae and their rigid fixation, they can therefore,at the same time unfortunately, hold the vertebrae apart while theresorption phase of the creeping substitution process forms gaps in thebone at the fusion site with the result that the desired fusion does notoccur. Such failure is known as pseudoarthrosis. When such a failureoccurs, the hardware itself will usually break or become loosened fromthe spine, thus requiring a further surgical procedure to remove thebroken components and another surgical procedure to again attemptfusion.

[0012] In response to the problems described above, a second generationof plating systems has been developed and/or proposed. These include asystem disclosed in U.S. Pat. Nos. 5,364,399 to Lowery and 5,423,826 toMorscher, as well as cervical spine locking plating systems offered bySYNTHES Spine, the DANEK ORION plate, the CODMAN SHURTLEFF plate, andthe SMITH NEPHEW RICHARDS plate, among others. The systems' formingmembers of this second generation have a number of common properties.They are all made of either a titanium alloy or pure titanium ratherthan stainless steel, to minimize adverse tissue reactions and are MRIcompatible, which stainless steel is not. The screws and the plates havebeen given increased thickness in order to achieve increased strength.The screws have larger diameters to improve their purchase withoutrequiring that they engage the posterior cortex of the vertebral bodies.Some mild longitudinal contouring of the plates is employed to allow forsome lordosis, and/or limited transverse contouring to better follow thegenerally curved aspect of the front of the vertebral bodies. Mechanismsare employed for securing the vertebral bone screws to their associatedplates in a manner to prevent the screws from backing out. While thissecond generation of plating systems represents a significantimprovement over earlier systems, certain existing problems persist,while new problems have been created.

[0013] For example, since the screws no longer extend into the posteriorcortex, it is common for the threads in the tapped screw hole to becomestripped and for the screws to fail to gain a suitable purchase. Inaddition, screw breakage continues to be experienced and occurs mostcommonly at the junction of the screw to the posterior aspect of theplate. The screws employed in both the SYNTHES system and the SMITHNEPHEW RICHARDS system are particularly vulnerable to this problembecause those screws are hollow at the level where they attach to theplate to permit the internal reception of locking screws.

[0014] In an attempt to prevent screw to plate junction breakage of thescrew, more recent designs of screws have an increasing root diameterfrom tip to head, which thus far has resulted in a near useless stubbyand blunt thread near the screw head with little holding power andlittle tactile feedback to the surgeon to signal the completion oftightening prior to stripping of the screw within the bone. Based onempiric studies testing these prior art screws, the use of a pretappedhole, rather than a self-tapping screw, was found to be preferred forpullout strength and thus these screws have not been self-tapping andthus the screw holes must be pre-tapped. Since the thread cuttingportion of a tap is necessarily sharp and rotated to work, there is aserious risk of damage to the surrounding soft tissues when it is used.This is compounded by the fact that the plates employed in these systemsdo not provide sufficient long axis contouring to make full allowancefor lordosis and do not have sufficient transverse contouring to preventrocking of the plate about its longitudinal axis and to conform to theanterior shape of the vertebral bodies, so that these plates do notprevent soft tissue from creeping in from the sides and beneath thescrew holes thus exposing these tissues to damage by the drill and thetap. While it is possible, at the time of surgery, to make some changein the contouring of these plates, this is generally limited tocontouring of the longitudinal axis and quite often causes distortion ofthe plate's bone screw holes and screw hole to plate junctions in amanner which has an adverse effect on the screw-plate interlock. Lack ofproper contouring prevents these plates from having an optimally lowprofile relative to the spine.

[0015] In some of the second generation cervical plating systems, screwbackout continues to occur, because these plates could not be designedto allow for the locking of all of the screws. Specifically, while thedesigners of these plates recognized the importance of securing the bonescrews to the plates, they were unable to lock all of the screws and hadto settle for leaving some of the screws unlocked.

[0016] Furthermore, several of these second generation systems utilizetiny and delicate “watchmaker” parts to achieve interlocking. Theseparts are characterized by the need to engage them with particularlydelicate small ended screw drivers. These interlocking components areeasily rendered ineffective by any effort to alter the contours of aplate during surgery.

[0017] Despite the improvement of these second generation platingsystems over the first problems, the problems still persist, the mostimportant of which is pseudoarthroses, and particularly “distractionpseudoarthroses”. Although these second generation plates have clearlyled to an increase in fusion rate, when a failure to produce fusionoccurs, it is generally accompanied by bone resorption along a line atthe graft-to-vertebra junction, which can be seen on a radiograph.

[0018] In the case of the weak first generation plates and screws, theplates might hold the vertebrae apart, preventing fusion, but only untilthe hardware would break, relieving the distraction, and then allowingthe fusion to occur. The second generation systems of plates are toostrong to allow this to occur, thus requiring further surgicalprocedures for the correction of the pseudoarthroses.

[0019] Compression plates are well known and are widely used inorthopedic surgery for the stabilization of tubular bones, and sometimesalso flat bones. Such plates may rely on some external compression meansor may be self-compressing, relying on the ability of the screw head toslide within a ramped slot such that the tightening of the bone screwsthrough the plate imparts a linear motion perpendicular to the screwaxes. U.S. Pat. No. 5,180,381 discloses an attempt to employ such amechanism in connection with anterior spinal fixation.

[0020] However, it has been found that all of the proposedself-compressing plating systems have in common the need for a screw toengage both a proximal and a distal cortex, (bone casing of very densebone material), so as to anchor the screw tip in a manner to allow theplate to move relative to the screw when tightened rather than allowingthe plate to drag the screw off axis. However, as already discussedearlier herein, when a screw is to engage the posterior cortex of thevertebral body, it is necessary for the drill and the tap which form thescrew hole, as well as the screw tip itself, to all enter the spinalcanal, thereby exposing the spinal cord to damage.

[0021] While the system disclosed in U.S. Pat. No. 5,180,381 avoids suchdanger by engaging the vertebral body end plate instead of the posteriorvertebral body cortex, the path of the screw is of necessity quiteshort, so that there is very little opportunity for the screw threads toachieve additional purchase within the vertebral body. It wouldtherefore appear that to the extent that the device disclosed in U.S.Pat. No. 5,180,380 is able to achieve its stated objectives, it wouldpull the front of the spine together more than the back and would notappear to compress the back of the vertebral bodies at all, thusproducing an undesirable iatrogenic loss of the normal cervicallordosis. Such a situation is disruptive to the normal biomechanics ofthe cervical spine and potentially quite harmful.

[0022] The creation of compression between adjacent vertebrae wouldoffer a number of advantages, including reduced distractionpseudoarthrosis, increased surface area of contact between the graft andvertebrae as slightly incongruent surfaces are forced together,increased osteogenic stimulation, since compressive loads stimulate boneformation, and increased fusion graft and spinal segment stability.

[0023] Among the new problems created by these second generation systemsis a tendency for the small “watchmaker” parts used to lock the bonescrews to the plate to fall off of the driver used for attaching thoseparts, or out of the associated plates and to become lost in the wound.In addition, these small parts are quite fragile and require specializedadditional instruments for their insertion and/or manipulation.Furthermore, incorrect bone screw placement relative to the axis of aplate hole may render the screw locking mechanism unworkable or maycause sharp and jagged shavings of titanium to be formed as a lockingscrew is driven into contact with an improperly seated bone screw. Themeans for establishing bone screw to plate hole alignment andpreparation are less than reliable. Furthermore, most of these secondgeneration systems lack a reliable and effective means for positioningand holding the plate during attachment.

[0024] Specific features of various prior art systems will be summarizedbelow.

[0025] The system disclosed in U.S. Pat. Nos. 5,364,399 and 5,423,826,cited earlier herein, includes a thin stainless steel plate which allowsfor side-by-side or offset bicortical screw placement, the plate havinga combination of screw holes and slots.

[0026] The “Acromed” system includes a titanium plate and screws whichrequire bicortical screw placement. This system does not include anylocking means for the bone screws.

[0027] The system disclosed in U.S. Pat. No. 5,180,381 includes an “H”shaped plate having a combination of ramped slots and a hole whichrequires bicortical screw placement at a 45N angle to the plane of theplate. This patent discloses that this angular positioning is for thepurpose of producing compression.

[0028] The SYNTHES Morscher plate system employs hollow, slotted screwheads. The screws are placed unicortically so that the heads, whenproperly aligned, come to rest in the upper portion of the plate holes.The upper portion of each screw is internally threaded to receive a tinyscrew which is screwed into the bone screw head in order to increase theinterference fit between the bone screw head and the wall of theassociated plate hole.

[0029] In the system disclosed in U.S. Pat. Nos. 5,364,399 and5,423,826, use is made of pairs of unicortical bone screws that may belocked in place at both ends of the associated plate by locking screwswhich have a small diameter shank and a large head. At each end of aplate two bone screws may be locked in place by a single locking screwwhich is situated between the bone screws. Generally, the plate isprovided, between its two ends, with a diagonal slot or slots forreceiving one or more additional screws, each additional screw beingsecurable in a bone graft or a respective vertebra which is spanned bythe plate. There is no locking screw associated with these intermediatebone screws to lock the bone screws to the plate.

[0030] The Codman Shurtleff plating system utilizes the side of apreinstalled rivet having a head rotatable to press against the side ofthe head of a bone screw so as to secure that one screw to the plate.The plates of this system also are provided with holes for receivingintermediate screws, but these screws are not associated with anylocking means.

[0031] While the designers of the last-mentioned systems recognized theimportance of locking the bone screws in position on their associatedplates, they did not provide for any locking of the intermediate bonescrews in their associated holes.

[0032] In an earlier version of the Codman Shurtleff system, the lockingmechanism was a lever pivotable about a shaft passing entirely throughthe plate and then flared so as to retain the shaft within the plate.The lever was rotated after the bone screw had been inserted to engagethe head of the bone screw and thus secure the bone screw to the plate.

[0033] Based on a consideration of the features of all of the knowncervical plating systems, it appears that there remains a need for animproved system having the following combination of features:

[0034] 1) The plate should be sufficiently strong to perform itsintended function without mechanical failure;

[0035] 2) The plate should be preformed in three dimensions so as toanatomically conform in both the longitudinal and transverse planes tothe anterior cervical spine;

[0036] 3) The plate should be constructed so that all of the bone screwsare generally perpendicular to the plate when viewed from the side, butpairs of screws are highly convergent corresponding to any vertebrallevel when viewed from the bottom, or on end;

[0037] 4) Each pair of screws engages in a respective vertebra and thehigh convergence of screws in a pair allows the length of the screwswhich engage the bone to be longer and still remain within that vertebraand provide a safer and stronger engagement with the vertebrae;

[0038] 5) The system should include bone screws which are capable ofachieving enhanced purchase within the bone of the vertebral body andwithout the need to penetrate the posterior vertebral cortex and enterthe spinal canal;

[0039] 6) Use should be made of a screw which is self-tapping, therebyeliminating the need for separate tapping steps;

[0040] 7) A reliable means should be provided for engaging andmanipulating the plate during installation;

[0041] 8) The plate should be engageable with an instrument means whichcan reliably produce bone screw holes which are coaxial with the screwholes in the plate;

[0042] 9) It should be possible to prepare the vertebral bone to receivethe bone screws so as to produce a stronger connection and a reduceddanger of thread stripping by means of a pilot hole punch creating apilot hole for the bone screws;

[0043] 10) Alternatively to the use of a pilot hole punch, a relatively(compared to the overall root diameter of the screw) small diameterdrill may be used to create the pilot hole.

[0044] 11) Means should be provided for locking each and every bonescrew in position relative to the plate, and the locking means should beof sufficient size and strength to reliably perform its intendedfunctions;

[0045] 12) Bone screw locking means should preferably be retainable bythe plate prior to bone screw insertion, or should be reliablyattachable to a driver to prevent any small parts from becoming loose inthe wound; and

[0046] 13) The system should be capable of effecting compression of thevertebral segments to be fused while maintaining and/or restoringlordosis.

OBJECTS OF THE INVENTION

[0047] It is an object of the present invention to provide an improvedanterior cervical plating system, installation instrumentation, andinstallation method which has the above described features and whichavoids many of the shortcomings of previously known systems.

[0048] One object of the present invention is to provide a lockingmechanism where a plurality of bone screws used for attaching the plateto the vertebrae can be easily and reliably locked in place at the sametime by a single operation.

[0049] Another object of the present invention is to provide a vertebralplate in which the locking mechanisms for locking the bone screws may bepre-installed by the manufacturer prior to the insertion of the bonescrews by the physician so that the physician does not have to attachthe locking mechanism to the plate as a separate procedure during theoperation.

[0050] Another object of the invention is to provide an anteriorcervical plating system which allows for the intersegmental compressionof the spinal segment (compression of the adjacent vertebrae and thefusion graft in the disc space between the adjacent vertebrae) inlordosis, and similarly, where desired, multisegmental compression.

[0051] A further object of the invention is to provide bone screws whichprovide for tactile feedback to the surgeon to assure sufficienttightening of the screws while avoiding stripping and are less prone tofailure by breakage or by loosening.

[0052] Another object of the invention is to provide bone screws whichachieve optimal purchase within the bone, without the need to penetratethe posterior cortex of the vertebrae.

[0053] A further object of the invention is to provide plates which aretextured or otherwise treated to promote bone growth from vertebrae tovertebra beneath the plate.

[0054] Another object of the invention is to provide a plate which isconstructed to reliably engage an instrument for forming all bone screwholes coaxial with the holes formed in the plate, the instrument havingintegral depth limiting means which completely eliminates the danger ofperforation of the posterior vertebral wall or entry into the spinalcanal.

[0055] Yet another object of the invention is to provide a system inwhich the bone screws and locking mechanisms, when fully installed, havea low profile.

[0056] It is another object of the present invention to provide for ananterior cervical plating system which is at least in partbioresorbable.

[0057] It is another object of the present invention to provide for ananterior cervical plating system comprising at least in part of boneingrowth materials and surfaces.

[0058] It is another object of the present invention to provide for ananterior cervical plating system comprising at least in part of bonegrowth promoting substances.

[0059] It is another object of the present invention to provideinstruments for reliably and easily performing the installation of theplates of the present invention.

[0060] It is still another object of the present invention to provide animproved method of installing the plates of the present invention.

[0061] The above and other objects and features of the invention willbecome more readily apparent from the following description of preferredembodiments of the invention, provided with reference to theaccompanying drawings, which illustrate embodiments of the inventionsolely by way of non-limiting example.

SUMMARY OF THE INVENTION

[0062] The plating system of the first preferred embodiment of thepresent invention comprises a plate having a length sufficient to span adisc space and to overlap, at least in part, at least two adjacentcervical vertebrae, a substantial portion of the lower surface of theplate preferably being biconcave, that is concave curved along asubstantial portion of the longitudinal axis of the plate and concavecurved along a substantial portion of the transverse axis of the plate.The lower surface of the plate may also textured and/or treated toinduce bone growth along the lower surface of the plate which contactsthe cervical vertebrae. The plate is provided with a plurality of bonescrew receiving holes which extend through the plate, from the uppersurface to the lower surface of the plate, and at least one lockingelement is associated with the bone screw receiving hole. The plate andits component parts, may be made of any implant quality materialsuitable for use in the human body, and the plate and associatedcomponent may be made of a bioresorbable material.

[0063] Bone screws are each insertable into a respective bone screwreceiving hole for attaching the plate to a vertebra. A locking element,is engageable to a locking element receiving recess and has a headformed to lock the bone screws to the plate. In the preferredembodiment, a single locking element locks a number of different bonescrews in place. The locking elements are pre-installed prior to use bythe surgeon in a manner so as to not impede installation of the bonescrews.

[0064] As a result, the problems previously associated with the lockingscrews of the type applied after the insertion of the bone screws,including the problems of instrumentation to position and deliver to theplate the locking means, backing out, breakage, stripping andmisthreading associated with the prior art more delicate locking screwsresembling “watchmaker's parts”, are eliminated.

[0065] In an alternative embodiment of the present invention, a lockingelement fits within a respective bone screw receiving hole to lock arespective one of the bone screws in place. According to this secondembodiment of the invention, each of the bone screws is locked to theplate by means of an individual locking element which bears against atleast a portion of the bone screw. Since no other holes need be formedin the plate to attach the locks to the plate, the plate remains quitestrong.

[0066] The locking elements can be in many forms to achieve theirintended purpose, such as, but not limited to, screws, threaded caps,rivets, set screws, projecting elements, and the like.

[0067] Also, a novel bone screw is disclosed so as to prevent pullingout of the bone screw during use. This is achieved by a design whichincludes a screw in which the outer diameter or crest diameter of thethread is maintained substantially constant along the entire length ofthe shaft of the bone screw, from below the head to above the tip, wherethreads of a lesser outer diameter facilitate insertion. The screw tipis fluted at its distal end to be self-tapping. The thread also has anextremely thin and sharp profile to cut into and preserve the integrityof the vertebral bone stock.

[0068] The plating system does not require that the head of the bonescrew be hollow, or that additional holes be placed through the plate inaddition to those provided for the passage of the bone screws. It willbe appreciated that bone screws are weakened when their heads are hollowand that plates are weakened when they are provided with additionalholes.

[0069] Additionally, the plate of the disclosed systems permit theproper aligning of the holes in the plate for the bone screws and forthe plate to be easily applied to the vertebrae in compression. Theplates include appropriate slots and engagement means for engagingcompression instrumentation, described in detail below, for applying acompression force between adjacent vertebrae to which the plate isattached, in a reliable and easy manner.

[0070] An improved locking screw driver is provided. The driver providesfor a wedged interference fit with a recess in the head of the bonescrews and the head of the locking elements. The same driver is usablefor both bone screws and locking elements. The driver ensures that thelocking element cannot fall off the driver and become lost in the wound.The driver has a tapered end to facilitate insertion into thecomplimentary recess in the head of the screws and is used to engage andpick up the locking elements. Alternatively, the receiving socket can betapered to the same purpose.

[0071] Alternatively, a combination bone screw and locking screw driveris disclosed in which the bone screw driver passes through alongitudinal opening in the locking screw driver so that both the bonescrew and the locking screw can be loaded prior to insertion of the bonescrew and both can be tightened with one instrument, without removing itfrom position.

[0072] Also, instruments are provided for forming pilot holes to assistin the ease and accuracy of the installment of the bone screws, and forcreating a creating a compression force between adjacent vertebraeduring installation of the plate and for holding the plate duringinstallation.

BRIEF DESCRIPTION OF THE DRAWINGS

[0073]FIG. 1 is a top perspective view of a first embodiment of acervical spine multiple locking plate.

[0074]FIG. 2 is a top plan view of the cervical spine multiple lockingplate shown in FIG. 1.

[0075]FIG. 3 is a side elevational view of the cervical spine multiplelocking plate shown in FIG. 1.

[0076]FIG. 4 is an end view of the cervical spine multiple locking plateshown in FIG. 1.

[0077]FIG. 5 is a bottom plan view of the cervical spine multiplelocking plate shown in FIG. 1.

[0078]FIG. 6 is a top plan view of the cervical spine multiple lockingplate shown in FIGS. 1-5, with locking elements installed in an openconfiguration.

[0079]FIG. 7 is a top plan view of a modification of the plate of FIGS.1-6 with a four bone screw locking element in place.

[0080]FIG. 8 is a top plan view of a further embodiment of a cervicallocking plate of FIG. 1 with an elongated central slot for increasedcompression capability.

[0081]FIG. 9 is a top plan view of a locking element for use with theplates of FIGS. 1-6.

[0082]FIG. 10 is a top plan view of a locking element for use with thecentral opening of the plate of FIGS. 7 and 22.

[0083]FIG. 11 is a top plan view of a locking cap for use in the endopenings shown in FIGS. 1, 6, and 7.

[0084]FIG. 12 is a side elevational view of the locking element of FIG.16.

[0085]FIG. 13 is a side elevational view of another embodiment of thelocking element of FIG. 16.

[0086]FIG. 14 is a top perspective view of an alternative embodiment ofcervical spine multiple locking plate for use with locking rivets.

[0087]FIG. 15 is a bottom plan view of the cervical spine multiplelocking plate of FIG. 14.

[0088]FIG. 16 is a top plan view of a two bone screw locking element.

[0089]FIG. 17 is a top plan view of an alternative embodiment of a fourbone screw locking element having head slits for increased flexibilityof the locking tabs.

[0090]FIG. 18 is a bottom plan view of a rivet type locking element foruse with the central opening of the plate of FIG. 14.

[0091]FIG. 19 is a side elevational view of a rivet locking element.

[0092]FIG. 20 is a top perspective view of the bottom portion of thehead of rivet of FIG. 19 viewed along lines 20-20.

[0093]FIG. 21 is a top perspective view of the head portion of a threebone screw locking element.

[0094]FIG. 22 is a top perspective view of a third embodiment of acervical spine multiple locking plate utilizing locking elements in theform of threaded caps.

[0095]FIG. 23 is a side elevational view of a locking element for usewith the plate of FIG. 22.

[0096]FIG. 24A is a side elevational view of a bone screw in accordancewith the present invention.

[0097]FIG. 24B is an enlarged side elevational view of the bone screw ofFIG. 24A.

[0098]FIG. 25 is a side elevational view of an alternative embodiment ofa bone screw in accordance with the present invention.

[0099]FIG. 26 is a bottom end view of the bone screw shown in FIG. 24A.

[0100]FIG. 27 is a top end view of the bone screw shown in FIG. 24A.

[0101]FIG. 28 is a top perspective view of a fourth embodiment of acervical spine multiple locking plate.

[0102]FIG. 29 is a top perspective view of a locking element for usewith the plate of FIG. 28.

[0103]FIG. 30 is a partial side sectional view of the plate of FIG. 28along lines 30-30 with a bone screw in place.

[0104]FIG. 31 is a top perspective view of the plate of FIG. 1positioned against the anterior aspect of three successive vertebralbodies in the cervical spine, a plate holder, and an instrument forforming bone screw receiving holes in to the vertebral bodies.

[0105]FIG. 32 is a cross-sectional view of a portion of the bone formingdevice shown in FIG. 31 viewed along lines 32-32.

[0106]FIG. 33 is a side elevational view in partial cross sectionillustrating a compression post tool and a compression post engaged toit for insertion into a vertebral body.

[0107]FIG. 34 is a side elevational view in partial cross section of thecompression post tool engaged for removal of the compression post fromthe vertebral body.

[0108]FIG. 35 is a bottom end view of the compression post tool of FIG.34.

[0109]FIG. 36 is a side elevational view of a plate engaging hook foruse with the compression apparatus shown in FIG. 38.

[0110]FIG. 37 is a cross-sectional view through the plate of analternative embodiment of a hole forming instrument in the form of adrill guide and drill for use during the plate installation procedure.

[0111]FIG. 38 is a side elevational view showing intersegmentalcompression of the spine and compression apparatus.

[0112]FIG. 39 is a view similar to that of FIG. 38 showing thecompression apparatus in a further stage of the plate installationprocedure.

[0113]FIG. 40 is a top perspective view showing the locking of the bonescrews to the plate.

[0114]FIG. 41 is a partial side sectional view of a locking elementattached to a driver instrument.

[0115]FIG. 42 is a partial side sectional view of another embodiment ofthe locking element attached to a driver instrument.

[0116]FIG. 43 is a partial cross-sectional view showing a cervicalplate, locking element, and bone screws along lines 43-43 of FIG. 40.

[0117]FIG. 44 is an enlarged portion of detail along line 44 of FIG. 43.

[0118]FIG. 45 is a side view in partial cross section of a plate holderattached to a plate.

[0119]FIG. 46 is a side view in partial cross section of anotherembodiment of a plate holder attached to a plate.

[0120]FIG. 47 is a top perspective view of a first embodiment of asingle locking plate.

[0121]FIG. 48 is a top plan view of the plate shown in FIG. 47.

[0122]FIG. 49 is a side elevational view of the plate shown in FIG. 47.

[0123]FIG. 50 is an end view of the plate shown in FIG. 47.

[0124]FIG. 51 is a bottom plan view of the plate shown in FIG. 47.

[0125]FIG. 52 is a top plan view of the plate shown in FIG. 47, withlocking elements in place.

[0126]FIG. 53 is a side elevational view of a bone screw used with theplate shown in FIG. 47.

[0127]FIG. 54 is a top end view of the bone screw shown in FIG. 53.

[0128]FIG. 55 is a bottom end view of the bone screw of FIG. 53.

[0129]FIG. 56 is a top plan view of a locking cap for use with thesingle locking plate of FIG. 47.

[0130]FIG. 57 is a side elevational view of the locking cap shown inFIG. 56.

[0131]FIG. 58 is a bottom plan view of the locking cap shown in FIGS. 56and 57.

[0132]FIG. 59 is a bottom perspective view of the locking cap of FIGS.56-58.

[0133]FIG. 60 is a top perspective view of the single locking plate ofFIG. 47 shown being held by a plate holder against three vertebralbodies, with the hole forming instrument for punching a pilot hole intothe vertebral bodies for receiving a bone screw.

[0134]FIG. 61 is a side elevational view in partial cutaway of the holeforming instrument threaded to a bone screw receiving hole.

[0135]FIG. 62 is a perspective side sectional view of the drill anddrill guide threadably engaged to the plate for drilling a hole forinsertion of a bone screw.

[0136]FIG. 63 is a top perspective view of a single locking plateinstalled along a segment of the spine with two locking caps installedin two bone screw receiving holes.

[0137]FIG. 64 is a side elevational view in partial cross section of alocking cap engaged to a driver for installing the locking cap.

[0138]FIG. 65 is a partial cross sectional view of the plate, bonescrews and locking caps along line 65—65 of FIG. 63.

[0139]FIG. 66 is an enlarged fragmentary view of area 66 of FIG. 65.

[0140]FIG. 67 is a perspective view of a cervical locking plate beingheld by an alternative plate holder instrument.

[0141]FIG. 68 is an end sectional view showing the plate holder of FIG.67 engaging a plate.

[0142]FIG. 69A is an end sectional view of an alternative embodiment ofthe plate holder.

[0143]FIG. 69B is an end sectional view of another alternativeembodiment of the plate holder.

[0144]FIG. 70 is a plate holder instrument with an offset and removablehandle.

[0145]FIG. 71 is a top perspective view of a second embodiment of acervical single locking plate having individual locking elements to lockeach bone screw.

[0146]FIG. 72 is a top perspective view of a threaded locking elementfor use with the cervical single locking plate of FIG. 71

[0147]FIG. 73 is a partial side sectional view of the plate of FIG. 71viewed along lines 73-73 with the locking element of FIG. 72 in place tohold a bone screw, but not fully tightened.

[0148]FIG. 74 is a top perspective view of an alternative lockingelement for use with a first modification of the cervical single lockingplate of FIG. 71.

[0149]FIG. 75 is a side sectional view of the first modification of theplate of FIG. 71 with the locking element of FIG. 74.

[0150]FIG. 76 is a perspective view of an alternative locking elementfor use with the first modification of the plate of FIG. 71.

[0151]FIG. 77 is a partial side sectional view of the first modificationof the plate of FIG. 71 with the locking element of FIG. 76 in place.

[0152]FIG. 78 is a top perspective view of another alternative lockingelement in the form of a rivet for use with a second modification of thelocking plate of FIG. 71.

[0153]FIG. 79 is a partial side sectional detail view of the plate ofFIG. 71 modified to use a locking element of FIG. 78 shown in place.

[0154]FIG. 80 is a partial cross sectional view of a plate and bonescrew with the end of a tool shown for use in inserting both the bonescrews and locking caps.

[0155]FIG. 81 is a side elevational view of another embodiment of thetool of FIG. 80.

[0156]FIG. 83 is a further embodiment of a cervical spine multiplelocking plate for use in stabilizing multiple segments of the spine.

[0157] FIGS. 84A-84E are various embodiments of cervical spine multiplelocking plates for use in stabilizing a single segment of the spine.

DETAILED DESCRIPTION OF THE DRAWINGS

[0158] The present invention will be described first in association withthe preferred embodiment of the plate system in which a plurality ofbone screws are locked in place with one locking element. This isreferred to as the multiple locking plate system. The multiple lockingplates will be described, then the locking elements for locking the bonescrews to the plate, then the bone screws associated with the multiplelocking plates, and finally the instrumentation and method ofinstallation of the multiple locking plates. Thereafter the platesystems in which a single locking element locks a single bone screw willbe described. This is referred to as the single locking plate system.The locking elements, bone screws, instrumentation, and method ofinstallation associated with the single locking plate will then bediscussed.

[0159] 1. Multiple Locking Plate System

[0160] The preferred embodiment of the multiple locking anteriorcervical locking plate 2 according to the present invention (here shownby way of example for use in a two level fusion (three adjacentvertebrae)) is shown in FIGS. 1-5. Plate 2 has a generally elongatedform whose outline generally departs from rectangular due to thepresence of lobes or lateral projections 4 at the corners and at thecenter of the sides of plate 2. Each lobe 4 has a rounded outline andcontains a respective circular bone screw receiving hole 6. Twoadditional intermediate circular bone screw receiving holes 8 arelocated inwardly of the sides of plate 2 and are centered on thelongitudinal center line of plate 2. Lobes 4 give plate 2 additionalstrength in the region surrounding each bone screw receiving hole 6. Itis recognized that other shapes for the plate 2 may be employed.

[0161] The intermediate paired bone screw receiving holes 8 are for usewith a two level (three vertebrae) fusion. The intermediate bone screwreceiving holes 8 may be eliminated for a single level (two vertebrae)fusion, or additional intermediate bone screw receiving holes 8 may beadded if additional levels are to be fused.

[0162] Plate 2 is further provided with three locking element holes 12,each of which in the preferred embodiment is internally threaded 3, andeach of which is surrounded by a shallow countersunk region 14. As willbe described in greater detail below, in the preferred embodiment, bonescrews are inserted in the bone screw receiving holes and a singlepre-installed locking element associated with each of the lockingelement holes 12 locks a number of bone screws 30 in position at onetime.

[0163] The number of paired bone screw holes generally correspond to thenumber of vertebrae to be fused. A plate for a one level fusion couldhave but a single locking element hole 12, while plates for fusing morethan two levels (three vertebrae) could have additional middle lockingelement holes 12 corresponding to additional paired bone screw holes. Inthe embodiment illustrated in FIGS. 1-6, each end locking element 20will lock three bone screws 30 in place, while the locking screw 21 inthe central locking hole 12 locks two bone screws 30 in place. As shownin FIG. 7, central locking element 25 can also be configured so thatfour bone screws 30 are locked at one time.

[0164] As shown particularly in FIGS. 3, 4 and 5, plate 2 is shaped sothat its bottom surface 27 (the surface which will be in contact withthe vertebral bodies) has a biconcave curvature, being concave both inthe longitudinal plane (corresponding to its length) and in the planetransverse thereto, corresponding to its width. The concave curvature inthe longitudinal plane conforms to the proper shape of the anterioraspect of the spine with the vertebrae aligned in appropriate lordosis.That longitudinal curve is an arc along the circumference of a circle(referred to herein as the “radius of curvature”) 15.0 cm to 30.0 cm inradius and more preferably 20.0-25.0 cm in radius. Viewed on end in FIG.4, the plate 2 has a radius of curvature of a circle 15-25 mm in radius,but preferably 19-21 mm in radius. While the plate 2 may have athickness between 2 to 3 mm, a thickness of between 2.25 and 2.5 mm ispreferred.

[0165] Having the bottom surface 27 of plate 2 contoured so that it isable to lie flush against the associated vertebral bodies is in contrastto conventional plates which have larger radii of curvature that contactthe vertebral bodies only along the longitudinal centerline of theplate, thereby permitting side-to-side rocking of the plate relative tothe vertebral bodies. The contour of the plate of the present inventionprovides effective resistance to rocking of the plate 2 relative to thevertebral bodies about the longitudinal center line of the plate,thereby reducing stress on the plate 2 and bone screws 30, andpreventing the soft tissues from becoming engaged beneath the plate.

[0166] Other advantages produced by the above curvature are that theplate 2 will conform more closely to the facing bone surface; the plate2 will project from the spine by a smaller distance; soft tissue will beprevented from sliding underneath the edges of the plate 2, where itcould be subject to damage; and the angle of the bone screws 30,perpendicular to the plate when viewed from the side, when installedwill be at a substantial converging angle, trapping the vertebral bonebetween the bone screws 30, and thus more strongly anchoring the plateto the spine.

[0167] As shown in FIG. 5, the bottom surface 27 of plate 2, preferablyhas a porous, roughened, and/or textured surface layer and may be coatedwith, impregnated with, or comprise of fusion promoting substances (suchas bone morphogenetic proteins) so as to encourage the growth of bonealong the underside of the plate 2 from vertebrae to vertebrae. Thetextured bottom surface 27 also provides a medium for retaining fusionpromoting substances with which the bottom surface 27 layer can beimpregnated prior to installation. The bottom surface 27 of plate 2 maybe given the desired porous textured form by rough blasting or any otherconventional technology, such as etching, plasma spraying, sintering,and casting for example. If porous, the bottom surface 27 is formed tohave a porosity or pore size in the order of 50-500 microns, andpreferably 100-300 microns. Fusion promoting substances with which theporous, textured bottom surface 27 can be impregnated include, but arenot limited to, bone morphogenetic proteins, hydroxyapatite, orhydroxyapatite tricalcium phosphate. The plate 2 may comprise of atleast in part a resorbable material which can further be impregnatedwith the bone growth material so that as the plate 2 is resorbed by thebody of the patient, the bone growth material is released, thus actingas a time release mechanism. Having the plate 2 being made from amaterial that is resorbable and having bone growth promoting materialpresent permits the vertebrae to be fused in a more natural manner asthe plate becomes progressively less load bearing thereby avoiding latestress shielding of the spine.

[0168] As further shown in FIGS. 4 and 5, at least one end of plate 2has a recess 18 that can cooperate with a compression apparatus,described in detail later in reference to FIGS. 36 and 38.

[0169]FIG. 6 is a top plan view of the plate 2 of FIG. 1 with lockingelements 20, 21 inserted into the locking element receiving holes. Inthe preferred embodiment, the locking elements 20, 21 are in the form ofscrews that cooperate with the threaded interior 3 of the locking holes12. Each of these locking elements 20, 21 is shown in its initial openorientation, where the orientation of the cutouts 22 in the head 23 ofeach locking element 20, 21 is oriented so as to permit introduction ofbone screws 30 into adjacent bone screw receiving holes 6,8 withoutinterference by the head 23 of the locking element 20, 21. It isappreciated that other configurations of the head 23 are possible so asto permit introduction of bone screw into adjacent bone screw receivingholes without interference by the head 23.

[0170]FIG. 8 is a top view of another embodiment of plate 2 of FIGS.1-5, and is generally referred to as plate 120. Plate 120 is providedwith a longitudinally extending elongated slot 122 along itslongitudinal axis which is superimposed on the middle locking hole 12.Elongated slot 122 allows additional relative movement between plate 120and a compression post 54 associated with a compression tool during thecompression procedure, as discussed below.

[0171] Referring to FIGS. 14 and 15, an alternative embodiment of amultiple locking plate referred to by the number 70 is shown. In plate70, rather than the threaded locking hole 12, a central opening 200 forreceiving a removable rivet 202, of the type shown in FIGS. 17-20, isprovided. FIG. 15 is a bottom plan view of the plate 70 shown in FIG.14. The contour of the plate 70 is the same as that of the plate 2 shownin FIGS. 1-5. The rivet 202 is removable and fits within the unthreadedopening 200, comparable to the locking hole 12 and slot 122 describedabove. Other embodiments may employ a rivet that is not removable, butis manufactured as part of the plate 70 as would be used in the endlocking holes 19 of FIGS. 14 and 15.

[0172] Referring to FIG. 22, another alternative embodiment of amultiple locking plate is shown and is generally referred to by thenumber 230. The plate 230 uses threaded caps, such as cap 300 shown inFIGS. 9 and 23, for a locking element or preferably one with cut outs asdescribed having an appearance in a top view such as the locking elementin FIGS. 10-11, for example. The central locking hole 232 has anelongated slot 234 for providing an increased compression capability, aswill be discussed further herein.

[0173] Referring to FIGS. 10-13, a first embodiment of a locking element20, 21, 25 in the form of locking screws according to the presentinvention for use with plate 2 is shown. FIG. 10 is a top plan viewwhich illustrates the head 23 of the central locking element 25 shown inFIG. 7. The shaft 46 of locking element 25 is threaded 47 to mate withthe threading 3 within the associated locking hole 12 of plate 2. Asshown in FIG. 21, each segment 49 on each side of cutouts 22 of thelocking element 21 has a bearing surface 48 formed at the lower surfaceof locking element head 23. As shown in FIG. 16, the locking elementhead 23 can be provided with two slots 42 for providing flexibility tothe locking element head 23 to assist in the locking element's abilityto ride over the top of the bone screw head 32 during the bearing actionwhen the locking element is rotated. Alternatively, it is appreciatedthat the bearing surface can be cammed, ramped or wedged. The cammed,ramped or wedged features can also be used with the other lockingelements described herein.

[0174] Referring to FIGS. 6 and 10-13, it will be appreciated that whenthe locking elements 20, 21 are rotated in the clockwise direction withrespect to the view of FIG. 6, a respective bearing surface 48 (as bestseen in FIG. 21) will ride upon the curved top surface 39 of arespective bone screw head 32 in order to positively lock the associatedbone screws 30 and the locking elements 20, 21 in place.

[0175] Alternatively, as shown in FIGS. 12 and 13 in place of a bearingsurface 48, a ramp or wedge shaped surface 44 may be used to increasethe force applied to the bone screw head 32. When locked, the leadingend of the ramped portion of the locking element would be lower than theprominence of the bone screw head 32 so that more force is needed tolift the locking element and untighten it than is needed for the lockingelement to remain tight and locked. However, the locking element heads23 need not have slots, be cammed, or have a ramped surface to achievethe locking of the bone screw 30 in place. Pressure, friction,interference fits, or other engagement means capable of preventing thelocking element from moving from its locked position may be employed.

[0176] The rivet 202, shown in FIGS. 17-20 is intended for use inassociation with plate 70 shown in FIGS. 14-15, is shown in detail incross section in FIGS. 19 and 20. The rivet 202 has a head 204, a shaft206, and an elongated bottom segment 208 for fitting within thecorresponding opening 200 in the plate 70. The lower surface 210 of thehead 204 of the rivet 202 has an irregular surface which may be cammed,such as on the bottom of locking element 20, 21, for engaging the topsurface 39 of the bone screw head 32. For use in the end locking holes19, the upper surface of the elongated bottom segment 208 can have anirregular surface for cooperating with the irregular surface of thebottom of the plate 70 to hold the rivet 202 in the locked positionagainst the bone screw head 32, as shown in FIG. 15. While the rivet ofFIG. 18 is a separate, removable component from the plate, the rivets,and particularly those for use with the end locking holes, can be formedas part of the plate during the manufacturing process of the plate andrivet can be non-removable.

[0177] Each of the above embodiments provides tight attachment of thelocking element relative the bone screw 30 and relevant plate.

[0178] In the alternative embodiment of multiple locking plate 23 shownin FIG. 22, the locking element can be in the form of threaded lockingcap 300 shown in FIG. 23. The threaded locking cap 300 has a thread 302on its outer circumference corresponding to the thread 303 on the innercircumference of the locking element depressions 304 in the top of theplate 230 shown in FIG. 22. The locking cap 300 is relatively thin,particularly compared to its width. The top 305 of locking cap 300 isprovided with a noncircular through hole 306 for receiving a similarlyconfigured driving tool.

[0179] Referring to FIGS. 28, 29, and 30 another embodiment of themultiple locking plate generally referred to by the number 400 and alocking element in the form of a thin locking member 412 are shown.Plate 400 has an opening in its top surface for insertion of the thinlocking member 412, a recess 402 associated with each of the bone screwreceiving holes 408 and a slot 410 in the side wall of the bone screwreceiving holes 408 to permit the thin locking member 412, having aseries of thin projections or blades 414, thinner than the slot 410,that give this locking member 412 an appearance similar to that of apropeller. The thin locking member 412 is able to be rotated within theplate so as to not cover the bone screw holes, thus allowing the thinlocking member 412 to be pre-installed prior to the installation of thebone screws by the surgeon. Limited rotation of the thin locking member412 allows the blades 414 to protrude through the slot 410 and to covera portion of the top of the associated bone screws 30. The blades 414 ofthe thin locking member 412 are flexible and, when rotated, slide overthe top surface 39 of the bone screw head 32 to lock the bone screw 30in place. As with the other embodiments discussed, each of theembodiments of the locking element is capable of locking more than onebone screw 30. It is appreciated that the various multiple lockingplates and locking element combinations are capable of locking as manyas four bone screws at once, but are equally effective for locking alesser number or none at all, that is securing itself to the plate.

[0180] It will be noted that one characteristic of each of the abovedescribed locking element embodiments is to have a driver engagementmeans, in these cases for example, a recess 24 as large as the recess 34in the bone screws 30 so that the same tool can be used to turn both thebone screws 30 and the locking elements. Also, the locking elements aresufficiently strong and have sufficient mass so as to be able towithstand being locked without breakage.

[0181] All of the shown examples of the multiple locking elements thathave a number of cutout portions have an arc with a radius greater thanthat of the bone screw head. In addition, the head 23 of each lockingelement 20, 21 is provided at its center with a noncircular recess 24,such as shown in FIG. 9 which is engageable by an appropriatemanipulation tool, such as shown in FIGS. 40-42. In the embodiment ofhead 23 shown in FIG. 9, the associated tool would have a hex head, butas discussed with regard to FIGS. 80 and 81, other shapes of recesses inthe head 23 may be used. The thread of each locking hole 12 and of eachlocking element 20, 21 has a close tolerance so that they will reliablyretain their orientations so as to permit introduction of bone screws 30into bone screw receiving holes 6, 8 without interference.

[0182] It is appreciated that while various forms of locking elementshave been disclosed, in light of the teaching, other equivalent meanscan be used for the purpose of locking the bone screws 30 in place. InFIG. 83, an alternative multiple locking plate 990 is shown havingadditional intermediate bone screw receiving holes 980 and associatedlocking elements 960 for locking bone screws 30 in place. Plate 990allows for a more close spacing and more pairs of bone screw holes thanthe number of vertebrae to be engaged.

[0183] In FIGS. 84A-84E various plates 700 a-g used for a single levelfusion are shown. Each of these plates 700 a-g is designed to span onespinal segment consisting of one disc space and two adjacent vertebrae(containing the bone graft), and have bone screws inserted into the endof the vertebrae through the bone screw receiving holes 6 associatedwith the two adjacent vertebrae and then locked in place. As shown inFIGS. 84A-84E, one locking element 710, or two locking elements can beused to lock four bone screws in place. In FIGS. 84A-84E, each of theplates 700 a-e is shown with the locking elements in their openorientation, before being rotated to lock the bone screws.

[0184] Each of the above described plates can have the same generallybiconcave contour as already described for conforming to the anterioraspect of the spine.

[0185]FIGS. 24A and 24B provide a side view of one embodiment of a bonescrew 30 according to the present invention. FIG. 27 is a top view ofthe bone screw 30. At the center of bone screw head 32 is a profiledrecess 34 which may have the same form as the recess 24 of each lockingelement 20, 21 in which case it may be turned with the same tool as thatemployed for turning locking elements 20, 21. It is appreciated that thedriver engaging portion of the bone screw 30 could be slotted, and beeither male or female (as is shown).

[0186] In the embodiment of bone screw 30 shown in FIGS. 24A and 24B,the bone screw head 32 is stepped, with the first lower head portion 35being contiguous with the screw shank 33 and has a smaller diameter thanthe upper portion of the bone screw head 32. When this embodiment ofbone screw 30 is employed, each bone screw receiving hole 6, 8 of theplate 2 has a countersunk region 14 matching the diameter of the upperportion of the bone screw head 32 and dimensioned for an interferencefit. The lower portion 35 of the bone screw head 32 is dimensioned toachieve an interference fit with its associated portion of bone screwreceiving holes 6, 8. The larger diameter upper portion of bone screwhead 32 assures that the bone screw 30 cannot be advanced completelythrough bone screw receiving holes 6, 8 of plate 2. The bone screw 30passes completely through the upper surface of the plate 2 withoutengaging the upper surface in any way.

[0187] As shown in FIG. 44, the head 32 of screw 30 passes unobstructedthrough the upper surface of the plate until the lower surface ofenlarged screw head 32 engages the upper face of the narrowed bone screwreceiving portion at the midsubstance or below the midsubstance of theplate. This is considered optimal for allowing for the greatest screw toplate stability, even absent the lock, against all forces except thosereverse the path of insertion, while still providing for the greatestplate strength beneath the bone screw head 23. That is, since the plateis of only generally 2-3 mm in thickness, a sheer verticalcircumferential wall is best able to constrain the motion of a screw ifthe head is similarly configured and there is little tolerance betweenthem. Placing the support of the head near the mid thickness of theplate is preferred as it allows the head to remain large to accommodatethe recess for the driver without being weakened, while placing thesupport of the head away from the upper surface of the plate allows thescrew head to be deep into the plate. Placing the support of the head atapproximately the mid thickness of the plate assures plenty of platematerial beneath the head to support while providing adequate headlength above and below the contact point to prevent the contact pointfrom acting as a fulcrum by providing adequate lever arms to preventunwanted motion.

[0188] In the alternative embodiment of bone screw 30′, as shown in FIG.25, bone screw head 32′ is tapered in the direction from the top of thebone screw head 32′ toward screw tip 36′. Again, the bone screw head 32′is dimensioned to achieve an interference fit in the associated bonescrew receiving hole 6,8 when the bone screw 30′ has been fullyinstalled. When this embodiment of bone screw 30′ is employed, bonescrew receiving holes 6, 8 need not be provided with a countersunkregion 4.

[0189] In each of the above embodiments of the bone screws, the bonescrews 30 and 30′ present a unique combination of a tapered screw shaft33 and a helical thread 31. The diameter of screw shaft 33 generallyincreases from a distal portion of the shaft near the screw tip 36toward the proximal portion of the shaft near screw head 32. In thepreferred embodiment, the rate of increase in diameter is also greaternear the bone screw head 32. Such a shape avoids stress risers andprovides increased strength at the screw-plate junction, where it isneeded the most. The tapering of screw shaft 33 may have a concave form,as shown in FIG. 24A, or may be linear. The distal portion of the screwshaft 33 may assume a constant diameter.

[0190] Referring again to FIGS. 24A and 24B, the thread 31 of the bonescrew 30 has a substantially constant outer, or crest, diameter “d” fromthe proximal portion of the shaft below the bone screw head 32 to thedistal portion of the shaft near the bone screw tip 36. In the screw tip36, the crest diameter of thread 31 may be reduced for preferably one totwo turns to facilitate the insertion and penetration of the bone screw30 into the bone.

[0191] In the preferred embodiment, the thread 31 of each bone screw 30has an outer diameter slightly smaller than the diameter of the lowestportion 35 of the bone screw head 32, which is adjacent the trailing, orupper, end of the associated thread 31. In addition, the thread 31 isrelatively thin, in the direction of the longitudinal axis of the screw,and tapers outwardly, and has a cross section of a triangle.

[0192] An example of the dimensions of a bone screw for use in humananterior cervical spinal surgery for insertion into the vertebrae is asfollows: the threaded portion of said screw has a length from about 10mm to about 22 mm (12-18 mm preferred) and a head length from about 1 mmto about 3 mm (2-2.5 mm preferred). The threaded portion should have amaximum outside diameter from about 3.6 mm to about 5.2 mm (3.8-4.5 mmpreferred) and the head has a diameter from about 3.8 mm to about 6 mm(4-5.5 mm preferred). The thread pitch is from about 1.25 mm to about2.5 mm (1.5-2.0 mm preferred) and has a sharp and thin threaded profile.The apex of the two faces of the thread have an angle of less than about21 degrees (15 degrees preferred) and the base of the thread is lessthan about 0.60 mm thick (0.25 mm-0.35 mm preferred). The screw has aroot diameter that increases from proximately above the tip of theshank, along the longitudinal axis to proximately below the head portionof the screw. Preferably, the tip of the screw tip is fluted by at leastone cut out section so as to make the screw self-tapping.

[0193] Even though the thread 31 of the bone screw 30 has a thinprofile, the thread will nevertheless be stronger than the bone intowhich it is introduced so that this thread will efficiently cut a thinhelical groove in the bone tissue. The volume of bone that will bedisplaced by the thickness of the thread is minimized by the thin formof the thread, yet the substantial crest diameter of the screw threadmaximizes the surface area of the threads in contact with the bone.While enlarging the screw shaft 33 diameter near the bone screw head 32increases its strength where needed, reducing the screw shaft 33diameter away from the bone screw head 32 where such strength is notrequired allows for the maximum area of engagement for the thread 31 tothe bone.

[0194] In the preferred embodiment, as shown in FIGS. 24A and 26, bonescrew tip 36 is provided with cutting flutes 38, to make the bone screw30 self-tapping. Unlike the prior art bone screws, used for anteriorcervical spinal surgery which are not self-tapping, the thread form ofthe present invention screw is itself more like a tap than aconventional screw in that the threads are very sharp and fluted.Additional embodiments of the bone screws 30 is shown in FIGS. 53-55.

[0195] By way of example, plates for fusing three adjacent vertebrae (2interspaces, or two spinal segments) are shown. Each set of the bonescrew receiving holes associated with a vertebrae is considered to be asegment of the plate so that for example, in FIG. 1 three segments areshown—an upper, a central, and a lower segment. While the presentdiscussion is in association with plates for use in fusing threevertebrae across two interspaces, it should be understood that longerand shorter plates having the appropriate number and location of bonescrew receiving holes corresponding to the number of vertebrae to befused are contemplated, and would take the form of the plates shown withfewer or more intermediate segments, such as the segment along line 9 ofFIG. 1, or the intermediate segments of the plates shown in FIGS.82-84F.

[0196] Referring to FIGS. 31-42, an outline of the steps of the methodfor installing the plates of the present invention is set forth below. Adetailed description of the instrumentation and method for installingthe plates of the present invention follows the outline.

[0197] Step 1

[0198] Having completed the interbody fusions, the surgeon removes anybone spurs or localized irregularities along the front of the spine ofthe area to be fused.

[0199] Step 2

[0200] The correct length plate is selected by the surgeon by measuringthe distance on the spine by a caliper, ruler, template, and the like.That plate having a length sufficient to span the distance of the spineto be fused and to partially overlap a portion of each of the endvertebrae to be fused.

[0201] Step 3

[0202] Utilizing a plate holder, the plate is placed into the wound andpositioned to confirm positioning, length, and screw hole alignmentrelative to the segments of the spine to be fused.

[0203] Step 4

[0204] As shown in FIG. 31, with the plate thus positioned and securelyheld, the plate may be attached to any of the vertebrae to be fused (byexample only, here shown as the top vertebra).

[0205] Sub-Step 4A

[0206] The pilot (guide) hole punch 60 is attached to the plate 2 as perFIG. 32, or alternatively, while not preferred the drill guide may beused as per FIG. 37. In either event, the pilot hole forming meansrigidly aligns with and is captured by the plate bone screw receivinghole wall.

[0207] Sub-Step 4B

[0208] The pilot hole is then formed by impacting the pilot hole punchof FIG. 32 or drilling with the drill of FIG. 37. In the alternativewhile not preferred, the formation of the pilot hole can be done awaywith altogether and the correct screw selected so as to have a lengthless than the distance along its path to the posterior vertebral cortexcan be directly inserted.

[0209] The determination of the appropriate screw length is made bymeasuring or templating from radiographs, MRI's, or CT scans, ordetermined directly by measuring the depth of the disc space.

[0210] Step 5

[0211] The correct screw is then attached to the screw driver whichregardless of the specific form of the screw driver engagement means, isdesigned to have an interference fit so as to remain firmly bound to thedriver during transport to the insertion site. FIGS. 41, 42, 63, 64, 80and 81 show various ways of achieving such a fit of the driver andscrew. In addition to a wedging at the screw and driver interface,clips, and springs and other means are well known for temporarily andreversibly securing the screw to the driver, such as is shown in FIG. 80where a slotted inwardly springing sleeve holds a threaded capperipherally until, as it is screwed into the plate, it is automaticallypushed back releasing the threaded cap.

[0212] Once a first bone screw has been fully inserted into a vertebrathrough the plate, it is preferable to insert the other of thetransverse pair in the manner already described as per FIG. 33.

[0213] In a similar manner, it is possible to insert the remaining bonescrews as per the surgeon's preference into each of the vertebrae to beincluded into the fusion, just the end vertebrae of the fusionconstruct, or additionally place screws into the fusion grafts.

[0214] However, as shown in FIGS. 33, 34, 38 and 39, it is possible withthe present invention at the surgeon's option to place any portion orall of the fusion construct under compression and to do sointersegmentally or across the entire length of the fusion constructeven when multi-segmented.

[0215] It is appreciated that the same procedure could be generally usedfor any of the plate systems of the present invention.

[0216] As shown in FIG. 31, the vertebrae 50 a-c are separated from oneanother by fusion graft blocks 51 which were previously installed in thespinal disc space between adjacent vertebrae 50 forming a fusion bonegraft construct. Plate 2 is shown in FIG. 31 with the locking elements20, 21 removed in order to simplify the illustration. It will beunderstood, however, that in the preferred embodiment the lockingelements 20, 21 can be, and preferably are, pre-installed in thepositions shown in FIG. 6 prior to positioning plate 2 upon vertebralbodies of the vertebrae 50, thereby saving the surgeon time and trouble.

[0217] Plate 2 may be held in position by any known plate holding means,but preferably by the holding tools shown in FIGS. 45, 46 or 70 by thenotches 142 in the sides of the compression arms 104, 130 of a vertebralcompressor tool 100 shown in FIG. 39, or as a further alternative, bythe unitary plate holder similar to the FIG. 70 design.

[0218] As shown in FIG. 45, plate holder 870 has a hollow tubularhousing 872, with a central rod 874 having a thread 878 at one end forengaging one of the threaded locking holes 12 in the plate 2. The bottomend of the housing 872 has projections 880, 882 that extend outwardlyand then downwardly to fit into the bone screw receiving holes 8 of theplate 2 preventing the housing 872 from rotating. The central rod 874 islocated in the housing 872 such that it can be rotated by rotating ahandle (not shown) which is fixed to the central rod 874 at its upperend.

[0219] In FIG. 46 an alternative embodiment of the plate holder 890 isshown. A single solid member 890 has a threaded projection 894 at itsbottom end for attachment to the central threaded locking hole 12 in theplate. The bottom surface of the holder 890 of this embodiment iscontoured so as to match the contours of the top surface of the plateadjacent to the locking hole 12, shown as a depression 14 (FIG. 1).

[0220] Referring to FIGS. 67-68, an embodiment of a plate holder forholding any of the plates while being positioned on the vertebrae isshown and generally referred to by the number 800. The plate holder 800has a hollow tubular housing 802, with a central rod 804 having a handle806 at one end and a thread 808 at its other end for engaging one of thethreaded locking holes 12 in the plate 600. The bottom end of thehousing 802 has projections 810, 812 that extend outwardly and thendownwardly 814, 816 to fit along the side edge of the plate 2 betweenthe end and intermediate lobes 4, preventing the housing 802 fromrotating. The central rod 804 is located in the housing 802 such that itcan be rotated by rotating the handle 806 which is fixed to the centralrod 804 at its upper end. This central rod 804 can also be attached tothe housing 802 so that it can move up and down to some extent, by anynumber of conventional ways, such as by having the central rod 804 havean annular depression with a length of approximately 3-5 mm, and a setscrew projecting inward from the housing to engage the central rod 804.Once the plate 600 is in the proper place and the plate is attached toone of the vertebrae by bone screws 30, the central rod 804 isdisconnected from the opening in the plate 600 and the holder 800 isremoved.

[0221]FIG. 69A is an alternative embodiment of the plate holder 850. Asingle solid member 852 has a threaded projection 854 at its bottom endfor attachment to the central threaded locking hole 12 in the plate. Thesolid member 852 could also be threaded into a bone screw receiving hole6. The bottom surface of the holder 850 of this embodiment is contouredso as to match the contours of the top surface of the plate adjacent tothe locking hole 12, shown as a depression 14 (FIG. 1).

[0222]FIG. 69B is another embodiment of the plate holder 850′. A housing851′ having an end 853′ configured to engage a bone screw receiving hole6 contains a rod 855′ having an uneven diameter and having a threadedportion 857′. As rod 855′ is rotated by a handle similar to handle 806shown in FIG. 68, rod 855′ screws downward into the housing 851′ intomatching threads 858′. As the end of rod 855′ is driven down, it spreadsportions 859 a′ and 859 b′ (859 c′ and 859 d′ not shown) wedging plateholder 850′ into a bone screw receiving hole of the plate. Plate holder850′ is best used with non-threaded bone screw receiving holes, butworks for all types of bone screw receiving holes.

[0223] Referring to FIG. 70, an alternative embodiment of the plateholder referred to by the number 800′ is shown in which there is aremovable handle 860 that is used for first attaching the plate holder800′ to the plate, by rotating the shaft 804, and then for holding theplate holder 800′ off to the side by extension 864, during theattachment procedure reducing the interference of the plate holder 800′with the surgical procedure.

[0224] Referring to FIG. 38, a compression tool 100 is shown with atoothed gear bar 102 having a first compression arm 104 secured to itsfree end. Compression arm 104 has at its distal end a bore 106 forremovably holding either a plate engaging element 108, shown in FIG. 36,having a hook 110 atone end for engaging a depression or notch 18 in theend of plate 2, or for removably holding a compression post 54 shown inFIGS. 33-34. As shown in FIG. 36, plate engaging element 108 includes ashaft 112 that will be inserted into the corresponding bore 106 ofcompression arm 104, and a flange 115 for resting against the bottomface of bore 106 to accurately limit the depth of insertion of plateengaging element 108 into the bore 106. A ring spring 128, preferably ofmetal, is located in an annular depression of the shaft 112, for holdingthe plate engaging element 108 in the bore 106.

[0225] Referring to FIGS. 38-39, compression tool 100 includes a secondmoveable compression arm 130 movable along toothed bar 102 parallel tofirst compression arm 104. The distal end of the second compression arm130 also has a bore 132, the same as bore 106, that can receive aremovable compression post 54. Bores 106 and 132 are the same so thateither compression arm 104, 130 can be used to hold the removablecompression post 54, permitting the compression tool 100 to be used inany orientation. By permitting the plate engaging element 108 and thecompression post 54 to both rotate and slide in the bores 106, 132 ofthe two compression arms 104, 130, with the plate engaging hook 110 ableto work even at an angle to the plate allows for the apparatus to bereadily attachable to the spine through the compression post 54 andplate.

[0226] Compression arm 130 has a driving assembly consisting of atoothed wheel (not visible) which is engaged with the tooth gear 138 ofbar toothed gear 102 and is connected to compression arm 130 such thatcompression arm 130 is movable along the length of toothed gear bar 102by means of the rotation of handle 140, which is connected to thetoothed wheel. When the handle 140 is turned in the direction of thearrow shown in FIG. 38, compression arm 130 is moved toward compressionarm 104. The driving assembly has a self lock release mechanism wherebythe movement of the two compression arms 104, 130 away from one anotheris prevented, without the activation of the release. On the inwarddistal end of each compression arm, on facing sides, is a notch 142 orrecess for holding the plate 2 along its sides between the central lobes4 and end lobes 4, as shown in FIG. 38.

[0227] While the toothed gear bar 102 and compression arms 104, 130 havebeen described as being straight, it is possible that the toothed gearbar 102 and compression arms 104, 130 may be arcuately or otherwiseshaped, so as to induce lordosis in the vertebrae, if so desired.

[0228] As shown in FIG. 31, in the event that the compression tool 100is used to hold the plate 2, the ends 144 of the compression arms 104,130 will be located in line with the fusion graft construct 51 which wasplaced in the disc space when plate 2 is properly positioned. A gap willexist between plate 2 and each fusion graft construct 51, providing aspace to accommodate the free ends of arms 104, 130 should they extendbeyond the bottom surface of the plate 2. As will be described below,the same compression tool 100 can also be used for compressing aplurality of cervical vertebral bodies with bone grafts interposedduring the attachment of plate 2 to the vertebrae 50.

[0229] Referring to FIG. 31, plate 2 is held by a suitable holder, inthis case shown as the compression arms 104 and 130. Once theappropriate length plate 2 has been properly positioned so that the bonescrew receiving holes 6 are aligned with each of the respectivevertebrae 50 a-c to be fused, the next step is the formation of bonescrew receiving holes 6 prior to installation of the bone screws 30themselves in the vertebrae 50 a. While the procedure is described asfirst attaching the plate 2 to the upper vertebrae 50 a, the plate 2 canbe attached to any of the vertebrae in any order. Different sized platesare used so that, as indicated above, the physician will select theappropriate sized plate in which the bone screw receiving holes 6, 8 arealigned with the three adjacent vertebrae 50 a, 50 b and 50 c. Pilotholes are formed by a pilot hole forming apparatus 60 shown in FIGS. 31and 32. Unlike with known prior art and screw plating systems, the bonescrews 30 may be inserted without the prior formation of an opening intothe vertebrae as the bone screws 30 are preferably sharp pointed,self-tapping, and have at their tip a diminishing major diameter toassist the screw entering and pulling into the bone. However, while ahole into the bone of the vertebrae may be formed prior to screwinsertion, it is preferable that the hole be of a smaller diameter thanthe root diameter of the screw and for a different purpose than with theprior art. With the prior art the hole drilled had to be of a diameterequal to but preferably larger than the root (minor) diameter of thescrew, as the screws were not self-tapping. It is desirous to createpilot holes to assure that a proper path for the bone screws 30 ismaintained, and also to prevent damage to the vertebral bone duringinsertion of the bone screws 30. In addition, the pilot hole formingapparatus 60 creates a more compact vertebral bone mass for reception ofthe self-tapping bone screw 30 used in this insertion.

[0230] As shown in FIGS. 31 and 32, pilot hole forming apparatus 60includes a hollow cylindrical housing 62 having a bottom provided with athrough hole 63. Housing 62 contains a central shaft 64 which extendsthrough the through hole 63 in the bottom of housing 62. The leading end66 of shaft 64 tapers gradually to a sharp point 65. Shaft 64 isprovided with a ring member 78 having a diameter which closelycorresponds to the inner diameter of housing 62 to guide the travel ofshaft 64 within housing 62. A compression spring 67 is interposedbetween the ring member 78 and the bottom of housing 62. Compressionspring 67 provides a bias force which normally urges the sharp point 65into a retracted position within housing 62. The upper end of shaft 64has an enlarged head 68 extending outside of the housing 62 which isintended to be manually depressed or struck by a percussion instrumentin order to drive the sharp point 65 out of housing 62 and into avertebral body 50 a. Shaft 64 is given a length, taking into account thelength that spring 67 will have when fully compressed, to determine themaximum depth of the pilot hole formed in a vertebral body. The depth isselected to assure that the pilot hole does not reach the posteriorcortex of the vertebral body, which borders the spinal canal.

[0231] Certain structural features of hole forming apparatus 60 areshown in greater detail in FIG. 32. In particular, it can be seen thatthe bottom end of housing 62 has a projecting portion 69 dimensioned tofit precisely in a bone screw receiving hole 6 or 8 of plate 2. Thebottom 71 of the projecting portion 69 is flat in a plane perpendicularto the axis of housing 62. When the projecting portion 69 of housing 62is snugly inserted into a bone screw receiving hole 6, 8 and the flatbottom 71 is placed flush against the upper surface of plate 2, it isassured that the leading end 66 of shaft 64 will form a pilot hole inthe vertebral bone having an axis perpendicular to the plane of theassociated portion of plate 2, thereby assuring that the bone screw 30will be subsequently installed so that its axis is also perpendicular tothe plane which is parallel to the upper and lower surfaces of theassociated portion of plate 2.

[0232] When a plate is used which has a threaded bone screw receivinghole, the lower end of the pilot hole forming apparatus 60 is threadedso as to engage the thread in the bone screw receiving hole 6, 8 therebyfixing the plate and the pilot hole forming apparatus together, assuringa stable fit between the pilot hole forming apparatus and the plate 2.It should be noted that the diameter of the leading end 66 of the shaft64 is small since it has to fit within the small space left between theinside wall of the pilot hole forming apparatus. Since it is only apilot hole for a self-tapping bone screw 30 that is being formed, thesmall diameter is satisfactory.

[0233] Referring to FIG. 37, if for any reason it should be desired toform the pilot hole in the vertebral body 50 by drilling, rather than bythe use of the pilot hole forming apparatus 60, use can be made of adrill guide 80, having a lower end as shown in FIG. 37. The drill 80guide consists of a tubular member 82 and a small diameter lower end 84which is dimensioned to achieve a precise interference fit in theassociated bone screw receiving hole 6, 8 of plate 2. Along the smalldiameter lower end 84, drill guide 80 has an axial end surface in aplane perpendicular to the longitudinal axis of the drill guide 80 sothat when the small diameter portion 84 is fitted into the bone screwreceiving hole 6 and the surface surrounding the small diameter portion84 is flush against the upper surface of plate 2, the axis of the drillguiding bore 86 in drill guide 80 will be precisely perpendicular to theupper and lower surfaces of the associated portion of plate 2. As withthe case described above, the bottom end of the drill guide 80 can bethreaded so as to engage to the threaded opening of plate 2.

[0234] After the bone screw receiving holes 6, 8 are formed in thevertebral body 50 a through the upper two bone screw securing holes 6 ofplate 2 by means of either hole forming apparatus 60 or drill guide 80,bone screws 30 are threaded into the vertebrae 50 while holding theplate 2 firmly against the vertebrae 50 with compression tool 100 orplate holder 800. This locks the plate to the vertebrae 50 a.

[0235] It is then possible, if desired, to compress the fusion graft inthe next adjacent vertebrae 50 b before attaching bone screws 30 to theadjacent vertebrae 50 b through the central bone screw receiving holesof plate 2. Once the initial bone screws are in place in the vertebrae50 a, the plate holder 100 or 800 may be removed from the plate 2. Thecompression of the fusion graft construct between the two adjacentvertebrae 50 a and 50 b is achieved as follows:

[0236] Compression post 54 is driven through the central locking hole 12of plate 2 by means of insertion tool 90, shown in FIGS. 33, 34 and 35,into the vertebral bone of vertebra 50 b, where it will be used in asubsequent step to apply a compression force between vertebrae 50 a and50 b. Compression post 54 consists of a shaft 56 having a sharp point 57at its lower end, an enlarged central collar 58 which serves as a depthstop, and a circumferential groove 59 proximate its upper end, definingan enlarged head 55.

[0237] Compression post insertion tool 90 consists of a shaft 92 havinga closed hollow portion 94 at its lower end 96 for receiving compressionpost 54 and an enlarged percussion cap 98 at its other end. Compressionpost insertion tool 90 also includes in its lower end 96 a secondopening 95 having a recess 99 in its inside wall for permittingengagement of the enlarged head 55 on the compression post 54 within thedepression 97. The second opening 95 is in communication with the hollowportion 94 of the insertion tool 90, as shown in FIG. 35.

[0238] Referring to FIG. 38, the bore 132 in the second compression arm130 of compression tool 100 is then applied over compression post 54 invertebrae 50 b, and the plate engaging element 108 is inserted in thebore 106 of the first compression arm 104 of compression tool 100. Thehook 110 of the plate engaging element 108 shown in FIG. 36 is fittedinto the notch 18 at the end of the plate 2 which is fixed by the bonescrews 30 inserted into the vertebra 50 a, as shown in FIG. 38. Asindicated above, however, the compression tool 100 can be rotated sothat the first compression arm 104 is now at the bottom and is able tofit over the compression post 54 in vertebrae 50 c.

[0239] Since the plate is attached to vertebrae 50 a by means of bonescrews 30 and compression post 54 is fixed to the adjacent vertebrae 50b, movement of the first and second compression arms 104 and 130 in thedirection of vertebrae 50 a by rotation of handle 140 results incompression of the bone graft construct 51 between the adjacentvertebrae 50 a and 50 b. The distance of several millimeters issufficient for compression of the bone graft construct 51. Once thedesired compression is obtained, bone screw pilot holes can be formed invertebral body 50 b by means of pilot hole forming apparatus 60, asdescribed above, for insertion of bone screws 30 into bone screwreceiving holes 8 of bone plate 2, fixing the plate 2 to the adjacentvertebrae 50 b. Compression tool 100 can then be withdrawn by activationof the release.

[0240]FIG. 39 illustrates the use of compression tool 100 to inducecompression between the lower two vertebral bodies 50 b and 50 c afterbone screws 30 have been installed in the middle vertebral body 50 b asjust described. As shown in FIG. 39, compression post 54 remains inplace in the middle vertebral body 50 b and an additional compressionpost 54 is driven into the lower vertebral body 50 c by means of pilothole forming tool 60 distal to the plate itself in the recess betweenthe end projections 4 to allow for the lower compression post 64 to bemoved towards vertebrae 50 b upwardly as shown. The original compressionpost 64 is inserted in bore 106 in the first compression arm 104 and theadditional compression post 54 is inserted into the bore 132 of thesecond compression arm 130 of compression tool 100. Again, as discussedabove, the turning of the handle 140 results in the two compression arms104, 130 moving towards one another, resulting in the compression post54 in vertebrae 50 c moving towards the upper compression post 54 invertebrae 50 b, once again compressing the fusion graft construct 51between vertebrae 50 b and 50 c. The upper compression post 54 invertebrae 50 b can not move since the vertebrae 50 b has been fixed tothe plate by the insertion of the bone screws 30 in the bone screwreceiving holes 8 of the plate 2. Thus, only the lower compression post54 and vertebrae 50 c can move. As before, the pilot holes associatedwith vertebrae 50 c are formed and the bone screws 30 are insertedthrough bone screw receiving holes 6. The compression tool 100 is thenremoved. Compression post 54 is then extracted from the vertebrae byinserting it in the second opening 95 of the compression postinsertion/removal tool 90, so that it engages the enlarged head 55 ofthe end of compression post 54 by depression 97, as shown in FIG. 34.

[0241] It is recognized that other variations in the order ofcompression may be employed. For example, during the compression of thefusion graft construct 51 between vertebrae 50 b and 50 c, the hook 110of plate engagement element 108 may engage the notch 18 in the end ofthe plate 2, and the other compression arm of the compression tool 100may engage the compression post 54 in the third adjacent vertebrae 50 c.It should also be noted that plate 2 has a recess end cut out portionbetween the lobes at the end of the plate for insertion of thecompression post 54 in the vertebrae. Otherwise, there may not be roombelow the end of the plate 2 for insertion of the compression post 54.

[0242] It will be noted that the above-described procedure will beperformed with the bone screws 30 fully inserted into vertebral bodies50 a, 50 b and 50 c and lordosis is maintained during compression of thebone graft construct 51.

[0243] As indicated above, the procedure for attaching the plate 2 tothe vertebrae 50 a, 50 b and 50 c was illustrated without the lockingscrews 20, 21 in place on the plate 2. FIG. 40 is a perspective viewshowing the plate 2 of FIGS. 1-5, at a stage of a surgical procedurewhen bone screws 30 have been fully installed in three adjacentvertebrae 50 a, 50 b and 50 c, and locking screws 20, 21 have beenrotated through an angle of about 90N to lock three bone screws 30 inplace; the left-hand locking screw 20 as viewed has been rotated throughan angle of about 60N to lock three bone screws 30 in place and thecentral locking screw 21 has been rotated through an angle of about 90Nto lock two other bone screws 30 in place. At this time, one of thecamming surfaces 44 of each locking screw 20, 21 rests atop the screwhead 32 of a respective bone screw 30.

[0244] Installation of the locking cap 300 can also be performed with atool 220 such as shown in FIGS. 41 and 42 having a suitably shaped tip222 with a length corresponding to the depth of hole 306 in a lockingcap 300. The end 222 of tool 220 is flared just proximal to the mostdistal end so that it creates a friction fit with the screw cap 300 forease of manipulation, and prevents the screw cap 300 from falling offthe tool 200.

[0245]FIG. 43 is a cross-sectional view in the plane of the center ofthe two end locking screw holes 6 of plate 2, with two bone screws 30 intheir installed positions and locking element 21 in its lockingposition. FIG. 44 is an enlarged view of one of the bone screws 30 inplate 2 of FIG. 43. In a preferred embodiment, the axis of each screw 30is generally perpendicular to tangents to the upper and lower surfacesof plate 2 at points which are intersected by the longitudinal axis ofthe associated bone screw 30. Thus, because of the curvature of plate 2in the plane of FIG. 43, bone screws 30 can be directed so as toconverge toward one another at a desired angle. Preferably, such anglewill be greater than 14°. More preferably, such angle will be greaterthan 14° and less than 30°. The axis of the two bone screws 30 shown inFIG. 43 may subtend an angle of about 45N. Alternatively, the curvatureof the plate from side to side may be so as to conform to the surface ofthe anterior aspect of the human adult cervical spine and the axis ofthe paired screw hole may deviate from being perpendicular to the platewhen viewed on end to achieve optimal convergence.

[0246] Because the bone screws 30, once inserted, are locked to theplate, a “claw” of a rigid triangular frame structure is obtained ateach pair of bone screws 30 such that the attachment of plate 2 to thevertebral bodies 50 a, 50 b and 50 c would be highly secure due to thetrapping of a wedged mass of bone material between the angled bonescrews triangle, even if any thread stripping should occur. The “claw”may be further formed by three angled bone screws in a tripodconfiguration or by four bone screws in a four sided claw configuration.

[0247] A plating system according to each of the above embodiments canbe installed in the same manner as described above, and using the sameinstruments and tools, as illustrated and described above with respectto the first embodiment. In the case of the embodiment shown in FIG. 22,the compression operations would be performed by means of slot 232instead of the middle locking screw hole 12.

[0248] 2. The Single Locking Plate Systems

[0249] The single locking plate system will now be described. FIGS.47-52 are views of a first embodiment of a single locking plate system.The contour of plate 600 is the same as the plate 2 shown in FIGS. 1-5.Plate 600 contains bone screw receiving holes 602 which are internallythreaded 603 for receiving corresponding locking elements in the form ofa locking cap 610, shown in FIGS. 56-59. For example, in plate 600, thebone screw hole 602 has an outer diameter of approximately 5 mm with apreferred range of 4-6 mm; and a threaded inner diameter ofapproximately 4.8 mm, with a range of 3.5-5.8 mm for this use. Attachingmeans other than threads may be used, such as bayonet type attachmentelements.

[0250] The bottom of each bone screw receiving hole 602 has an inwardlystepped portion of properly selected dimensions for retaining anassociated bone screw 170, as shown in FIGS. 53-55. As described ingreater detail below, in this embodiment, a single locking element inthe form of a locking cap 610 having threads 608 shown in FIGS. 56-59,is associated with each of the bone screws receiving holes 602.

[0251] The difference between the bone screw 170 used in the singlelocking embodiment of the plate from the bone screw used in associationwith the multiple locking plate is essentially due to the fact thatwhereas in the multiple locking plate embodiment the locking elementsslide over a portion of the top 39 of the screw head 32, in the singlelocking embodiment the locking cap 610 fits over the head 172 of thebone screw 170. Therefore, the head 172 of the bone screw 170 of thepresent embodiment need not be smooth. This permits the head 172 of thisembodiment bone screw 170 to be thicker and stronger.

[0252]FIG. 65 shows two bone screws 170 and associated threaded lockingcaps 610 in their fully installed positions. In these positions, headportions 174 and 176 of each bone screw 170 form an interference fitwith corresponding portions of an associated bone screw receiving hole602. Rim 612 of each threaded locking cap 610 forms an interference fitwith upper portion 178 of the head of its associated bone screw 170.Because the thread 608 of each locking cap 610 mates precisely with theinternal thread in an associated bone screw receiving hole 602, eachthreaded locking cap 610 is additionally subjected to a clamping forcebetween associated head portion 178 and the internal threads 603 ofassociated bone screw receiving hole 602. The rounded head 614 of eachthreaded locking cap 610 assures that the upper surface of an assembledplating system will be free of sharp edges, or projections.

[0253] Referring to FIGS. 80 and 81 tools for use in inserting both thebone screws and the locking cap in the single locking plate 600 areshown. In the first embodiment of the driving tool 1000 shown in FIG.80, the tool 1000 has an outer tubular housing 1002. Within the housing1002 is a torks type or hexagonal driver 1004 that has a projecting end1006 that corresponds to the recess 306 in the cap 610 for engagementwith the cap 610. As indicated above, the driver 1004 is configured sothat it makes a firm attachment for the locking cap 610 for holding thelocking cap 610 firmly to the driver. The hex driver 1004 is hollow soas to be able to permit the shaft 1010 of a Phillips or torks screwdriver to fit through the hollow portion 1012 for engagement by its tip1012 with the corresponding recess 180 of bone screw 170 for engagementby the end 1006 of the driver 1004. The shaft 1010 of the driver 1000 islonger than the tubular housing and driver 1004 has an upper end (notshown) extending from the top end of the tubular housing 1002 so that itcan be rotated by the handle.

[0254] The housing 1002 has a diameter that permits the locking cap 610to be held within the inner end of the tubular housing 1002 by afriction fit or to the driver 1004. It is appreciated that other methodsof holding the locking cap 610 within the end of the tubular housing1000 may also be employed.

[0255] As shown in FIG. 80, the operation of the bone screw and lockingelement driver 1000 is as follows: the cap 610 is inserted onto the endof the cap driver 1004, and then the cap driver 1004 with the shaft 1010of the bone screw driver passing through the central longitudinalopening of the cap driver. As shown, the bone screw driver shaft 1010passes through the recess 306 in the cap 610 and engages the recess 180in the head of the bone screw 170. The bone screw 170 is shown beinginstalled in a bone screw receiving hole in the plate 600. The handle(not shown) of the bone screw driver is rotated, thereby screwing thebone screw 170 in place. Since the diameter of the bone screw driver isless than the width of the recess 306 of the cap 610, the bone screwdriver shaft 1010 is able to rotate without rotation of the cap 610.

[0256] The hollow tubular housing 1002 rests on the top surface of theplate 600 and assists in the alignment of the shaft 1010 in relationshipto the plate. Once the bone screw 170 is inserted, the cap driver 1004is depressed until the threads 608 on the outside of the cap 610 engagesthe threads 603 of the bone screw receiving hole. The cap driver 1004 isthen turned until the cap 610 is securely locked in place.

[0257] In FIG. 81, an alternative embodiment of the combination bonescrew and locking cap driver is shown. In this embodiment, a housing isnot used. Instead, the driver shaft 1010 holds the cap 610 by frictionand the handle 620 for the bone screw driver shaft 1010 is rotated. Aball spring assembly 622 holds the cap driver 1002 up until the bonescrew has been screwed into the bone screw receiving hole. Driver 1010has an elongated portion that once the bone screw has been installed,the ball spring 622 is depressed and the handle 624 associated with thecap driver is permitted to descend for rotation of the cap 610. Atubular housing can be employed to assist in aligning of the cap 610 inthe bone screw receiving hole, as indicated above.

[0258] The drivers shown in FIGS. 80 and 81 simplify the procedure, andreduce the number of instruments that are necessary to be used duringthe installation procedure. The procedure is quick and reliable, givingthe physician more assurance that small watch parts will not be lost ordifficult to manipulate.

[0259]FIG. 52 is a top view of the plate 600 partially installed, withthreaded locking caps 600 installed in bone screw receiving holes 602.

[0260] FIGS. 53-55 show a bone screw 170 for use with the single lockingplating system according to the invention. Bone screw 170 differs frombone screw 30 previously described in detail, only with regard to thestepped configuration of head 172. Preferably, bone screw 170 includes alower portion 174 which is contiguous with the screw shank and has areduced diameter equal to the maximum diameter of the shank 176. Portion178 of head 172 also has smaller diameter than lower portion 174. Thethread 182 has the same configuration as for the bone screw 30 discussedabove. However, either embodiment of bone screws can be used with any ofthe plates.

[0261] As in the case of the multiple locking plating system describedabove, the bone screws 170 for use in the single locking plating systemare preferably solid, where the screws adjoin the lower plate surface,where screws used with prior art plates are most prone to breakage, theonly recess in the heads being for engagement of the tip 222 of drivingtool 220 and with the recess being above the critical area. Therefore,these bone screws 170 remain robust. The screw heads are not deeplyslitted into portions and the locking caps do not impose a radial outerforce on the associated bone screw heads so the screw heads do notspread apart so as to be stressed and weakened.

[0262] Referring to FIGS. 71, 73 and 75 another alternative embodimentof the single locking plate system of the present invention is shown andreferred to by the number 500. The plate 500 has the same contour as theplate 2 shown in FIGS. 1-5, but associated with each of the bone screwopenings 502, are threaded openings 524 offset from the bone screwopenings 502 for receiving the locking element 506, 508, shown in FIGS.72 and 74 as a threaded locking set screw or cap 506 or screw 508.

[0263] It is appreciated that other configurations of single lockingplates may be employed. Referring to FIG. 82, a single locking plate 900is shown in which there are a pair of bone screw receiving holes 910 atits ends 930 and a number of bone screw receiving holes 950 along thelongitudinal axis of the plate 900. The additional bone screw receivingholes 950 permit a single plate to be able to be aligned with a numberof different sized vertebrae disc spaces, and bone fusion grafts. Asindicated above, the plate of the present invention shown in FIGS. 1-5,requires that a properly sized plate be selected by the surgeon so thateach pair of bone screw receiving holes 6, 8 line up with theappropriate vertebrae. This requires a number of different sized platesto be available for optimum attachment of the bone screw receiving holesto each of the vertebrae. With the plate 900 of FIG. 82, the closespacing and increased number of central openings permit the surgeon tolocate at least one appropriate opening to be aligned with each of theintermediate vertebrae, and/or bone grafts.

[0264] The procedure for installation of the single locking plates issubstantially the same as described herein in detail for the multiplelocking plates. The central longitudinal slot 670 in the single lockingplates is used for the compression procedure. The same instrumentationis used to create the plate hole either by means of a punch or a drill.FIGS. 60-69 show the various steps in the procedure for installation ofthe single locking plates, comparable to the steps employed in theinstallation of the multiple locking plates.

[0265] Referring to FIGS. 76-79 the heads 507 and 526 of the lockingelements 508 and 522 have a recess 510 and 524 corresponding to theradius of the bone screw openings 502 and 528 so that the lockingelement 508 and 522 may be installed in place prior to the insertion ofthe bone screw 170 into the bone screw receiving hole 502 and 528. Whenthe locking elements 508 and 522 are rotated, a portion of its headextends over the top of the head of bone screw 170 to lock it in place.As with the above embodiments, the bottom surface of the locking screws508 and 522 can have a camming or other configuration for engagementwith the top surface 39 of the associated bone screw 170.

[0266] While the plate instrumentation and method have been described inassociation with attaching a plate to the vertebrae of the spine, itshould be appreciated that the plates can be adopted for specificationto other parts of the body. See, for example, application Ser. No.09/022,344, filed Feb. 11, 1998, and titled Skeletal Plating System, nowU.S. Pat. No. 6,139,550, incorporated by reference above. However, thedimensions of the plate, the specific contours and placement of the bonescrew receiving holes would have to be modified.

[0267] Similarly, the bone screws described in this application could beused in other parts of the body, again being modified so as to servetheir intended purposed, depending on the size of the body part in whichthey are to be installed.

[0268] While particular embodiments of the present invention have beenshown and described, it will be obvious to those skilled in the art thatchanges and modifications may be made without departing from thisinvention in its broader aspects and, therefore, the aim in the appendedclaims is to cover all such changes and modifications as fall within thetrue spirit and scope of this invention.

[0269] While specific innovative features may have been presented inreference to specific examples, they are just examples, and it should beunderstood that various combinations of these innovative features beyondthose specifically shown are taught such that they may now be easilyalternatively combined and are hereby anticipated and claimed.

What is claimed is:
 1. A plating system, comprising: an anteriorcervical plate adapted to be applied to the anterior human cervicalspine, said plate having a lower surface adapted to contact the anterioraspect of at least one cervical vertebral body and an upper surfaceopposite said lower surface, at least one bone screw receiving holeextending from said upper surface through said lower surface, said bonescrew receiving hole being adapted to receive at least one bone screwfor engaging the cervical vertebral body to attach said plate to thecervical spine; and a bone screw adapted to attach said plate to thecervical vertebral body, said bone screw comprising: a leading end forinsertion into the cervical vertebral body, a trailing end opposite saidleading end, and a mid-longitudinal axis; a head adapted to blockfurther forward motion of said screw through said bone screw receivinghole of said plate, said head having an upper portion and a lowerportion, each of said upper and lower portions having an upper facingsurface oriented at least in part toward said trailing end of saidscrew, said upper portion being configured to cooperatively engage adriver instrument adapted to insert said screw into the vertebral body,said upper and lower portions of said head each having a cross sectionaldimension transverse to the mid-longitudinal axis of said screw, saidcross sectional dimension of said upper portion being less than saidcross sectional dimension of said lower portion, said upper facingsurface of said lower portion of said head being at least in part in aplane that crosses the mid-longitudinal axis of said screw; a tip atsaid leading end of said screw; a shaft between said tip and said head,said shaft having a root diameter, said shaft having a first shaftportion proximate said tip and a second shaft portion proximate saidhead, the root diameter of said first shaft portion being less than theroot diameter of said second shaft portion; and a thread along at leasta portion of said shaft, said thread adapted to engage the bone of thecervical vertebral body.
 2. The plating system of claim 1, wherein saidlower portion of said head has a bottom surface oriented toward saidleading end of said screw that is at least in part flat and generallytransverse the mid-longitudinal axis of said screw.
 3. The platingsystem of claim 1, wherein said upper and lower portions of said headeach have a length parallel to the mid-longitudinal axis of said screw,the length of said upper portion being greater than the length of saidlower portion.
 4. The plating system of claim 1, wherein said upper andlower portions of said head each have a length parallel to themid-longitudinal axis of said screw, the length of said upper portionbeing less than the length of said lower portion.
 5. The plating systemof claim 1, wherein said head and said shaft each have a length parallelto the mid-longitudinal axis of said screw, the length of said headbeing less than one-half the length of said shaft.
 6. The plating systemof claim 1, wherein said head is configured to form an interference fitwith said bone screw receiving hole of said plate.
 7. The plating systemof claim 1, wherein said head has a cross sectional profile along themid-longitudinal axis that is stepped.
 8. The plating system of claim 1,wherein said cross sectional dimension of said lower portion of saidhead is configured to prevent said screw from passing completely throughsaid bone screw receiving hole of said plate.
 9. The plating system ofclaim 1, wherein said shaft has a maximum root diameter and said crosssectional dimension of said lower portion of said head is greater thanthe maximum root diameter of said shaft.
 10. The plating system of claim1, wherein said shaft has a maximum root diameter and said crosssectional dimension of said upper portion of said head is less than themaximum root diameter of said shaft.
 11. The plating system of claim 1,wherein said head comprises a recess configured to cooperatively engagea tool for installing said screw.
 12. The plating system of claim 11,wherein said recess is hex-shaped.
 13. The plating system of claim 1,wherein said head is configured not to substantially protrude beyondsaid bone screw receiving hole when installed in said plate.
 14. Theplating system of claim 1, wherein said head is substantially solid. 15.The plating system of claim 1, wherein at least a portion of said headis solid in a plane transverse to the mid-longitudinal axis of saidscrew.
 16. The plating system of claim 1, wherein said head isconfigured to cooperatively engage a locking element for retaining saidscrew to said plate.
 17. The plating system of claim 1, wherein said topsurface of said lower portion of said head is configured tocooperatively engage a locking element for retaining said screw to saidplate.
 18. The plating system of claim 17, wherein said upper portionhas a side surface generally parallel to the mid-longitudinal axis ofsaid screw that is configured to cooperatively engage the lockingelement.
 19. The plating system of claim 1, wherein said root diameterof said shaft is curved along at least a portion of the length of saidshaft in a direction between said head and said tip along themid-longitudinal axis of said screw.
 20. The plating system of claim 1,wherein said root diameter of said shaft is at least a portion of aconcave curve.
 21. The plating system of claim 1, wherein said rootdiameter has a greater rate of increase proximate said head of saidscrew.
 22. The plating system of claim 1, wherein said second shaftportion has a generally circular cross section.
 23. The plating systemof claim 1, wherein said second shaft portion is generally conical. 24.The plating system of claim 1, wherein said first shaft portion has agenerally circular cross section.
 25. The plating system of claim 1,wherein said first shaft portion is generally cylindrical.
 26. Theplating system of claim 1, wherein said tip is at least one of pointed,tapered, and coned.
 27. The plating system of claim 1, wherein said tipis configured to be self-tapping.
 28. The plating system of claim 27,wherein said tip includes at least one of a pointed tip, cutting flutes,and decreased thread height.
 29. The plating system of claim 1, whereinsaid tip includes cutting flutes that interrupt at least one turn ofsaid thread proximate said tip.
 30. The plating system of claim 1,wherein said thread has an outer diameter that diminishes proximate saidtip.
 31. The plating system of claim 1, wherein said thread has amaximum outer diameter in the range of 3.6 mm to 5.2 mm.
 32. The platingsystem of claim 1, wherein said thread pitch is in the range of 1.25 to2.5 mm.
 33. The plating system of claim 1, wherein said thread hasopposed side faces being angled relative to each other to form an apexof said thread, said side faces forming an included angle in the rangeof 11 degrees to 30 degrees.
 34. The plating system of claim 1, whereinsaid thread has opposed side faces, said side faces being angledrelative to each other to form a base at said root diameter of saidshaft and a crest opposite said base, said side faces having a thicknesstherebetween in the range of 0.25 mm to 0.60 mm at said base.
 35. Theplating system of claim 1, wherein said screw has an overall length inthe range of 10 mm to 22 mm.
 36. The plating system of claim 1, whereinsaid head has a length parallel to the mid-longitudinal axis of saidscrew in the range of 1 mm to 3 mm.
 37. The plating system of claim 1,wherein said head has a length parallel the mid-longitudinal axis ofsaid screw in the range of 2 mm and 2.5 mm.
 38. The plating system ofclaim 1, wherein at least a portion of said plating system comprises atleast in part of one of bone and bone growth promoting material.
 39. Theplating system of claim 38, wherein said bone growth promoting materialis selected from one of bone, bone derived products, bone morphogeneticprotein, and hydroxyapatite.
 40. The plating system of claim 1, incombination with a bone growth promoting material.
 41. The platingsystem of claim 40, wherein said bone growth promoting material isselected from one of bone, bone derived products, bone morphogeneticprotein, and hydroxyapatite.
 42. The plating system of claim 1, whereinat least a portion of said plating system is treated with a bone growthpromoting substance.
 43. The plating system of claim 1, wherein at leasta portion of said plating system is at least in part resorbable.
 44. Theplating system of claim 1, wherein at least a portion of said platingsystem is formed of a porous material.
 45. The plating system of claim1, wherein at least a portion of said plating system is treated topromote bone ingrowth between said plate and the adjacent vertebralbodies.